The invention relates to glaze-stable colored pigments based on platelet-type substrates coated with metal oxides which are stable in decorative colors engobes, glazes and enamels.
Many pigments which are incorporated into glazes, enamels or similar materials, are known. However they suffer from a number of drawbacks. Thus, many of them are unstable at the normal firing temperatures of about 700.degree.-800.degree. C., since they are strongly attacked by the aggressive molten fluids. Again, others contain a high proportion of environmentally dangerous heavy metals, for example cadmium, in order to ensure a stable coloration, for example in the yellow and red color region.
A need has therefore arisen for pigments which do not have the above drawbacks or have them only to a small degree.
Platelet-type pigments, coated with metal oxide, which contain in the outer coating alkaline earth metal oxides or hydroxides, e.g., in an amount of 0.1-5% by weight are known from the U.S. Pat. No. 4,435,220.